The present invention relates generally to reducing power consumption in portable electronic devices such as radiotelephones. More particularly, the present invention relates to controlling the duration of a low-power sleep mode in a radiotelephone.
Many communication devices are portable and operate on battery power. An example of such a communication device is a radiotelephone. A radiotelephone is a mobile or portable radio which provides two-way radio communication with fixed radio equipment in a radiotelephone system. To improve portability and user convenience, the radiotelephone is powered by a rechargeable battery.
One design goal for radiotelephones is minimization of power consumption from the battery. This permits use of physically smaller, lighter batteries. Further, power consumption reduction extends the operating time of the radiotelephone. Reduced power consumption is very important in a consumer product such as a radio telephone.
To minimize power consumption it is known to place the radiotelephone in a low-power sleep mode. In such a mode, power is removed from all unnecessary circuitry. The sleep mode is extended for as long as possible while ensuring the liable information.
Many radiotelephones must be synchronized with the timing of the system in which they operate. Synchronization is necessary, for example to locate and read a paging channel broadcast by the system to indicate an incoming call for the radiotelephone. Thus, there is a need to retain or recover timing information even while in the low-power sleep mode.
Accordingly, there is a need for an improved method and apparatus for maximizing duration of sleep mode while ensuring synchronization with system timing upon exiting the sleep mode.